Aircraft need to produce varying levels of lift for take-off, landing and cruise. A combination of wing leading and trailing edge devices are used to control the wing coefficient of lift. The leading edge device is known as a slat. On larger aircraft there may be several slats spaced along the wing edge. During normal flight the slats are retracted against the leading edge of the wing. However, during take-off and landing they are deployed forwardly of the wing so as to vary the airflow across and under the wing surfaces. The slats usually follow an arcuate or curved path between their stowed and deployed positions. By varying the extent to which the slat is deployed along said path, the lift provided by the wing can be controlled.
An assembly is required to support and guide movement of a slat between stowed and deployed positions and a typical arrangement showing a cross-section through part of a wing 1 and a slat 2 in its stowed position is illustrated in FIG. 1. As can be seen from FIG. 1, the slat 2 is provided with an arcuate support arm or slat track 3 one end 4 of which is rigidly attached to the rear of the slat 2 and extends into the wing 1. The slat track 3 penetrates machined rib 5 and wing spar 6 forming the wing structure. The slat track 3 defines an arc having an axis and is mounted within the wing so that it can rotate about that axis (in the direction indicated by arrows “A” and “B” in FIG. 1) to deploy and retract the slat 2 attached to one end of the slat track 3.
To drive the slat rack 3 so as to deploy or retract the slat 2, a toothed slat rack 7 having an arcuate shape corresponding to the arcuate shape of the slat track 3 is mounted within a recess 3a on the slat track 3 and a correspondingly toothed drive pinion 8 is in engagement with the teeth 7a on the slat rack 7 so that when the drive pinion 8 rotates, the teeth 8a on the drive pinion 8 and the teeth 7a on the rack 7 cooperate to pivot or drive the slat rack 7 and the slat attached thereto, into a deployed position, i.e. in the direction of arrow “A” in FIG. 1. Typically, the slat track 3 rotates through an angle of 27 degrees between its fully stowed and fully deployed positions. Rotation of the pinion 8 in the opposite direction also drives the slat track 3, in the direction of arrow “B”, back into its stowed position, as shown in FIG. 1.
The drive pinion 8 is mounted on a shaft 9 that extends along, and within, the leading edge of the wing 1. Several gears 8 may be rotatably mounted on the shaft 8, one for driving each slat 2 so that when the shaft 9 is rotated by a slat deployment motor close to the inboard end of the wing 1, all the slats are deployed together.
The slat track 3 has a generally square cross-sectional profile such that its upper and lower surfaces 3b, 3c each define a portion of a curved surface of a cylinder each having its axis coaxial with the axis of rotation of the slat track 3.
The slat track 3 is supported between roller bearings 10a, 10b both above and below the slat track 3 and the axis of rotation of each bearing 10a, 10b is parallel to the axis of rotation of each of the other bearings 10a, 10b and to the axis about which the slat track 3 rotates in the direction of arrows “A” and “B” between its stowed and deployed positions. The upper bearings 10a lie in contact with the upper surface 3b of the slat track 3 and the lower bearings 10b lie in contact with the lower surface 3c so that they support the slat track 3 and guide it during deployment and retraction. The bearings 10a, 10b resist vertical loads applied to the slat 2 during flight both in stowed and deployed positions and also guide movement of the slat track 2 during slat deployment and retraction.
It will be appreciated that the bearings 10a, 10b resist loads that are applied in the vertical direction only. By vertical loads are meant loads that act in a direction extending in the plane of the drawing or, in a direction acting at right-angles to the axis of rotation of each bearing.
It will be appreciated that there can be significant side loads acting on a slat 2 in addition to loads acting in a vertical direction during flight, especially as the slats 2 generally do not extend along the leading edge of the wing 1 exactly square to the direction of airflow. By side-loads is meant loads that act in a direction other than in a direction that extends in the plane of the drawing or, in other words, those loads that act in a direction other than at right-angles to the rotational axis of each bearing 10a, 10b. 
To counteract side-loads, the slat track 3 is also supported by further bearings 11 disposed on either side of the slat track 3 as opposed to the vertical load bearings 10 mounted above and below the slat track 3. These side-load bearings 11 may not be rotational and may just comprise bearing surfaces, pads or cushions against which the side walls of the slat track 3 may bear when side loads are applied to the slat 2.
It is also conventional to provide at least one failsafe shaft 12, commonly referred to as a “funk pin” between each of the upper bearings 10a and which are positioned so as to support the slat track 3 in the event that one or more of the vertical load bearings 10 fail. The funk pins 12 may be non-rotatable shafts against which the slat track 3 slides or skids in the event of failure of a bearing 10. During normal operation the funk pins perform no function and a clearance gap exists between each pin and the surface of the slat track 3 so that the slat track 3 does not contact the funk pins except in the event of a bearing failure.
It will be appreciated that space for components within the wing structure close to the leading edge of the wing 1 is very limited, especially once the slat track 3 together with its vertical and side load bearings 10a, 10b,11, the drive pinion 8 and the funk pins 12 have all been installed. The requirement to house all these components places considerable design restrictions on the shape of the wing 1 in addition to increasing weight, manufacturing costs and complexities.
As the additional side-load bearings 11 and funk pins 12 are disposed between each of the upper and lower bearings 10a, 10b, these bearings must be spaced from each other in the circumferential direction about the axis of the slat track 3 by a distance which provides sufficient space between the bearings 10a, 10b to receive the side-load bearings 10a, 10b and the funk pins 12. As a consequence of this, a further disadvantage with the conventional assembly is that the slat track 3 must be relatively long to accommodate the desired maximum deployment angle for the slat 2 whilst ensuring that the slat track 3 is adequately supported by two vertical load bearings 10a above the slat track 3 and two vertical load bearings 10b below the slat track 3, even at maximum deployment. As a result of its extended length, the slat track 3 penetrates the spar 6 and so the free end of the slat track 3 must be received within a track can 13 that separates the slat track 3 from the fuel stored within the wing 1 behind the spar 6. However, it is undesirable to have openings in the spar 6 as this can weaken the wing structure. It will also be appreciated that the requirement for a track can 13 also presents additional problems and assembly issues with the need to provide an adequate seal where the track can 13 is attached to the spar 6 so as to prevent fuel leakage.
Embodiments of the invention seek to provide an aircraft slat support assembly that overcomes or substantially alleviates the problems referred to above.